Tissues samples
This study was approved by People’s Hospital of Yangxin County. A total of 60 BC patients were recruited at People’s Hospital of Yangxin County. BC tumor tissues and adjacent normal tissues were obtained and stored at -80°C until use. Informed consent was obtained from all patients.
Cell culture and transfection
Human BC cells (MCF-7 and MDA-MB-231) and normal breast epithelial cells (MCF-10A) (ATCC, Manassas, VA, USA) were cultured in RPMI-1640 medium (Gibco, Grand Island, NY, USA) containing 10% FBS (Gibco) and 1% Penicillin/Streptomycin (Sangon, Shanghai, China) at 37°C in 5% CO2. Cell transfection could be carried out by Lipofectamine 3000 (Invitrogen, Carlsbad, CA, USA). Circ_0000732 small interfering RNA (si-circ_0000732) or lentivirus short hairpin RNA (sh-circ_0000732), miR-1253 mimic or inhibitor (anti-miR-1253), pcDNA COL11A1 overexpression vector (pcDNA-COL11A1), and their controls were constructed by Ribobio (Guangzhou, China).
Quantitative real-time PCR (qRT-PCR)
Total RNA was isolated by TRIzol reagent (Invitrogen), and cDNA was obtained by PrimeScript RT Reagent kit (Takara, Dalian, China). The synthesized cRNA was used for qRT-PCR with SYBR Premix Ex Taq (Takara) in PCR system. Primer sequences were listed in Table 1. The β-actin or U6 was used as internal control and the relative expression was calculated by 2–ΔΔCt method. In subcellular localization analysis, the nuclear RNA and cytoplasm RNA of BC cells were isolated by PARIS Kit (Invitrogen). Then, circ_0000732 expression in BC cell nuclear and cytoplasm was detected.
Table 1
Primer sequences used for qRT-PCR
Name
|
|
Primers (5’-3’)
|
hsa_circ_0000732
|
Forward
|
GGGCCACTGATGACTCCTTC
|
Reverse
|
CTGCAGCTTCATCCTGGACA
|
COL11A1
|
Forward
|
GGTGATCCCAAGGCAGCATA
|
Reverse
|
AGCCACTGTCCTCATCTTCT
|
miR-1253
|
Forward
|
GTATGAGAGAGAAGAAGATCAG
|
Reverse
|
CTCAACTGGTGTCGTGGAG
|
β-actin
|
Forward
|
CTCCATCCTGGCCTCGCTGT
|
Reverse
|
GCTGTCACCTTCACCGTTCC
|
U6
|
Forward
|
CTCGCTTCGGCAGCACA
|
Reverse
|
AACGCTTCACGAATTTGCGT
|
Cell counting kit 8 (CCK8) assay
After transfection, BC cells were harvested and re-seeded in 96-well plates. After culturing at indicated time periods, CCK8 solution (Beyotime, Shanghai, China) was added into each well and cultured for 4 h. Optical density (OD) value was analyzed by microplate reader at a wavelength of 450 nm.
Edu assay
Edu Cell Proliferation Kit (Sangon) was used in accordance with the kit instructions. Briefly, transfected BC cells were seeded into 24-well plates. The cells were stained with Edu solution, fixed with paraformaldehyde, treated with Triton X-100, and then hatched with DAPI solution. The fluorescence signal was captured under the fluorescence microscope, and relative Edu positive (Edu+) cells were counted.
Transwell assay
BC cells suspended with serum-free medium were plated into the upper of 24-well transwell chamber (Corning Inc., Corning, NY, USA) coated with or without Matrigel (for invasion and migration, respectively). The lower chambers were filled with complete medium. After 24 h, the migrated and invaded cells were fixed with paraformaldehyde and stained with crystal violet. Cell images were observed under a microscope (200 ×), and the number of cells was counted in 5 fields randomly.
Western blot (WB) analysis
Total protein was extracted by RIPA lysis buffer (Beyotime). After resolved by SDS-PAGE gel, proteins were transferred to PVDF membrane followed by blocked with skimmed-milk. Membrane was hatched with primary antibody and secondary antibody one by one, and then the protein blot was visualized using BeyoECL Moon (Beyotime). The antibodies (Abcam, Cambridge, MA, USA) were listed as below: anti-E-cadherin (1:5,000, ab40772), anti-N-cadherin (1:1,000, ab18203), anti-Vimentin (1:1,000, ab45939), anti-OCT4 (1:1,000, ab19857), anti-NANOG (1:2,000, ab109250), anti-CD133 (1:1,000, ab19898), anti-COL11A1 (1:500, ab64883), anti-β-actin (1:1,000, ab8227) and Goat Anti-Rabbit IgG (1:50,000, ab205718).
Sphere formation assay
After transfection, BC cells were harvested and re-seeded into ultra-low attachment 6-well plates (1×103 cells/well) with serum-free medium containing 20 ng/mL EGF, 1:50 B27, and 20 ng/mL bFGF. 10 days later, the sphere state was observed under a microscope (100 ×), and the number of spheres (>100 μm) was counted to calculate sphere formation efficiency.
Dual-luciferase reporter assay
Starbase3.0 software and Targerscan software were used to predict the binding sites between miR-1253 and circ_0000732 or COL11A1 3’UTR. According to this, the circ_0000732-WT/MUT vectors and COL11A1 3’UTR-WT/MUT vectors were generated using pmirGLO vectors. The vectors were transfected with miR-1253 mimic /miR-NC into BC cells using Lipofectamine 3000. 48 h later, Dual-luciferase Reporter Gene Assay Kit (Beyotime) was used for analyzing relative luciferase activity.
Mice xenograft models
BALB/c nude mice (n = 5/group; Vital River, Beijing, China) were subcutaneously injected with MCF-7 cells (2×106) stably transfected with sh-NC or sh-circ_0000732. Every 7 days, tumor volume was calculated until 35 days. After the mice were sacrificed, the tumor tissues were weighted. Then, the tumor tissue was used to prepare paraffin sections for Ki67 immunohistochemical (IHC) staining. Animal experiments were approved by People’s Hospital of Yangxin County.
Statistical analysis
Results were denoted as the mean ± SD. GraphPad Prism 7.0 software was used for statistical analysis. Differences between groups were analyzed by Student’s t-test or ANOVA. Pearson correlation analysis was used to analyze the linear correlation. P < 0.05 was considered as statistically significant.